Conventionally, there are optical information recording/reproducing devices which record information on information recording regions (information recording planes) of optical information recording media (optical disks) of reflection systems such as CDs (Compact Disks) and DVDs (Digital Versatile Disks), and/or reproduce the information recorded on the information recording regions.
Also, in recent years, reflection-system disks having recording density of approximately 50 GB have been commercially available even in consumer fields based upon the Blu-ray Disk (will be referred to as “BD” hereinafter) standard using blue-purple semiconductor lasers, the HD DVD (High Definition DVD) standard, and the like. On the other hand, as to optical disks, larger storage capacities have been expected which are comparable with storage capacities (100 GB to 1 TB) of HDDs (Hard Disk Drives).
However, in order to realize such ultra-high density with employment of optical disks, novel storage technologies are required, while the novel storage technologies are different from the conventional high density technologies by which wavelengths of optical elements are shortened and NAs of objective lenses are increased. As a consequence, in recent years, an attention has been paid to hologram recording technologies for recording digital information by utilizing the holography. In accordance with the hologram recording technologies, two-dimensional information can be simultaneously recorded/reproduced by a single hologram. Also, a plurality of page data can be overwritten in the same place. As a result, the above-described hologram recording techniques are advantageous for a large capacity of information can be recorded and/or reproduced in high speeds.
As such hologram recording technologies, a so-called “angular multiplex recording system” (refer to, for instance, JP-A-2004-272268) has been proposed. In the angular multiplex recording system, signal luminous fluxes are collected by a lens onto a hologram-purpose optical disk (will be referred to as “hologram disk” hereinafter), and at the same time, reference light of collimated luminous fluxes are irradiated so as to be caused to interfere with the signal luminous fluxes in order to perform hologram recording, and moreover, different page data are displayed on a spatial light modulator so as to perform multiplex recording while an incident angle of the reference light with respect to the hologram disk is changed.
Also, another hologram recording technique using a shift multiplexing system (refer to, for example, WO2004-102542) has been proposed. In the shift multiplexing system, while light from pixels of an inner side in a single spatial light modulator is employed as signal light and light from ring belt-shaped pixels of an outer side thereof is employed as reference light, both the luminous fluxes are collected onto a hologram disk by the same lens, and the signal light is caused to interfere with the reference light in the vicinity of a focal plane of the lens so as to record a hologram.